Recently, minimally invasive approaches have been developed to facilitate catheter-based implantation of valve prostheses on the beating heart, intending to obviate the need for the use of classical sternotomy and cardiopulmonary bypass. These techniques include a transapical approach for aortic valve replacement, typically involving the use of an introducer port, i.e., a large-bore overtube, of a trocar. A crimped, stented valve prosthesis reversibly coupled to a delivery catheter is transcatheterally advanced toward the native valve, where it is either forcefully deployed using a balloon catheter, or, alternatively, passively deployed using a self-expandable system.
The need to position the crimped valve at the orifice of the native aortic valve for deployment may lead to one or more of the following complications: (1) a reduction in cardiac output secondary to the obstruction of the native valve's orifice by the crimped stented valve prosthesis, until the prosthesis is fully expanded and operative; (2) a substantial increase in left ventricular afterload caused by the obstructed aortic orifice, which may result in left ventricular pump failure; and/or (3) device embolism or migration during deployment of the prosthesis, caused by a forceful left ventricular contraction against the valve prosthesis during attempted stent expansion and deployment.
Several techniques have been used to reduce the likelihood of these complications. For example, rapid right ventricular pacing induces a transient hemodynamic cardiac arrest. This technique is intended to avoid an excessive increase in afterload during the deployment of the valve prosthesis, and also to reduce the risk of device migration during deployment. However, rapid ventricular pacing deliberately causes a drop in cardiac output, albeit temporarily, which may be poorly tolerated by patients suffering from heavily hypertrophied hearts, reduced left ventricular function, and/or coronary artery disease. Alternatively, extracorporeal or intracorporeal bypass or assist devices have been used, which may further complicate the procedure significantly due to their complexity. For example, advancing part of the tubing system of the intracorporeal bypass into the pulmonary veins requires first creating a large-bore hole in the atrial septum which later needs to be closed with an occluder device. Extracorporeal bypass systems, such as ECMO (extracorporeal membrane oxygenator) may be associated with vascular, hematological and rheological complications.
U.S. Pat. No. 7,201,772 to Schwammenthal et al., which is incorporated herein by reference, describes a prosthetic device including a valve-orifice attachment member attachable to a valve in a blood vessel and including a fluid inlet, and a diverging member that extends from the fluid inlet. The diverging member includes a proximal end near the fluid inlet and a distal end distanced from the proximal end. A distal portion of the diverging member has a larger cross-sectional area for fluid flow therethrough than a proximal portion thereof. The diverging member may have a diverging taper that causes fluid to flow therethrough with pressure recovery at the distal end thereof.
PCT Publication WO 06/070372 to Schwammenthal et al., which is incorporated herein by reference, describes apparatus including a prosthetic device having a single flow field therethrough, adapted for implantation in a subject, and shaped so as to define a fluid inlet and a diverging section, distal to the fluid inlet. The prosthetic device includes a plurality of axially-extending struts which extend along at least a portion of the diverging section and diverge outwardly, such that distal ends of the struts are spaced further from one another than proximal ends of the struts throughout a cardiac cycle of the subject. The diverging section includes a diverging envelope coupled to the struts, which is adapted to assume an open position thereof during systole, permitting blood flow through the device, and which is adapted to collapse to a closed position thereof during diastole, inhibiting blood flow through the device.
PCT Publication WO 05/002466 to Schwammenthal et al., which is incorporated herein by reference, describes prosthetic devices as described for use in the treatment of aortic stenosis in the aortic valve of a patient's heart. The prosthetic device has a compressed state for transarterial delivery, and is expandable to an expanded state for implantation. The prosthetic device includes an expandable metal base constructed so as to be implantable in the expanded state of the prosthetic device in the aortic annulus of the aortic valve; and an inner envelope lining tune inner surface of the metal base. The inner envelope, in the expanded state of the prosthetic device, extends into the aorta and is of a diverging conical configuration, in which its diameter gradually increases from its proximal end within the aortic annulus to its distal end extending into the aorta, such as to produce, during systole, a non-turbulent blood flow into the aorta with pressure recovery at the distal end of the inner envelope. Preferably, the distal end includes a prosthetic valve which is also concurrently implanted, but such a prosthetic valve may be implanted separately in the aorta. Also described are preferred methods of implanting such prosthetic devices.
The following patents, all of which are incorporated herein by reference, may be of interest:    U.S. Pat. No. 6,395,026 to Aboul-Hosn et al.    U.S. Pat. No. 6,935,344 to Aboul-Hosn et al.    U.S. Pat. No. 6,532,964 to Aboul-Hosn et al.